Neptune is a single-player modification for Half-Life 2, taking place entirely outside the mother game's universe. Set primarily onboard a mysterious and desolate cruise liner, floating in the middle of the Atlantic Ocean, Neptune allows the player to slowly unravel the dark and disturbing past of the ship as he/she explores its once-grand rooms, corridors, concert halls, restaurants, bars and maintenance areas.
Taking influence from games such as System Shock 2, BioShock, Thief: Deadly Shadows and Silent Hill, Neptune is an atmospheric, narrative-driven, horror-based shooter; an exercise in videogame storytelling and tense level design.
It is expected to be released in Q3 2009.